On high-output three-layer coex blown film lines used for flexible food packaging sealant webs, the resin is placed in the sealant layer at a thickness contribution of 18–25 µm within a 60–80 µm total lamination. The line is configured with a 350 mm spiral mandrel die, 2.0 mm die gap, and 30:1 L/D barrier feed screws. FLEXUS VLDPE 5020 is characterized by a nominal density of 0.902 g/cm³ (ASTM D1505) and melt index of 0.8 g/10 min (ASTM D1238, 190°C/2.16 kg). The extruder profile is run from 160°C at the feed throat to 185°C at the die, with melt pressure at the screen changer held between 180 bar and 260 bar. To suppress bubble flutter above 45 m/min, 25 wt% LDPE extrusion homopolymer is added to the sealant layer; the remaining 75 wt% is FLEXUS VLDPE 5020. The LDPE raises melt strength without eliminating the low seal initiation. Seal strength is tested by ASTM F88/F88M using a dwell of 0.3 s and nip pressure of 0.4 MPa; hot tack is tested by ASTM F1921 at a seal bar temperature of 100°C. The sealant layer meets 21 CFR 177.1520(c) and Regulation (EU) No 10/2011 as a food-contact olefin polymer, provided migration testing is completed on the finished printed laminate under the intended food simulants. Finished goods made from this structural layer include frozen food pouches, fresh produce pillow packs, and stand-up pouches for dry foods.

What Property Transition Occurs When the Sealant Web Runs at −25°C on a Vertical Form-Fill-Seal Line?

Vertical form-fill-seal lines running IQF vegetables, frozen meat, and frozen seafood expose the pouch film to seal jaw temperatures of 110–135°C and filling temperatures down to −30°C. The sealant film is produced at 50–70 µm thickness from 100% FLEXUS VLDPE 5020 or an 80/20 blend with a fractional-melt octene LLDPE. The low crystallinity of the VLDPE phase results in a seal initiation temperature roughly 8–12°C lower than that of a conventional butene LLDPE with the same melt index; this is a measurable reduction on the VFFS control setting. The lower set point reduces transverse seal shrink-back and burn-through at dwell times of 0.2–0.5 s. Puncture resistance is controlled by ASTM D5748; the film is required to survive protrusion from sharp-edged frozen vegetables without pinholes. Dart impact is measured by ASTM D1709-A after conditioning at −25°C for 48 h. The major processing conflict is the narrow window between adequate seal strength and film distortion: the seal-bar temperature must be held within ±5°C at high line speeds, otherwise cold seals or edge puckering occur. Dye penetration testing by ASTM F1929 and burst testing by ASTM F2054 are used for finished pouch release. The terminal product is a high-abuse frozen food pouch with a minimum seal strength commonly specified at 4 N/25 mm after conditioning at −25°C.

When Stretch Exceeds 120% in Automated Hooding Lines, VLDPE Layer Distribution Dictates Puncture Retention

Stretch hood films are processed on monolayer and three-layer blown film lines with die gaps of 1.8–2.5 mm, blow-up ratios of 2.8–3.5, and frost line heights of 800–1200 mm. FLEXUS VLDPE 5020 is introduced as a core or secondary skin layer at 20–40 wt% of the total formulation; the remaining fraction is a higher-density butene or hexene LLDPE. The low density reduces machine-direction secant modulus to approximately 150 MPa or lower (ISO 527-3), allowing pre-stretch ratios above 120% without stress whitening. The skin layer must contain a slip and antiblock package reduced to 0.1–0.3 wt% because additive migration from the 0.902 g/cm³ phase is faster than from a 0.918 g/cm³ LLDPE; excessive slip addition destroys the cling needed for pallet stability. On a high-speed hooder applying 200–250% pre-stretch, the stretched film is required to retain at least 70% of its original dart impact (ASTM D1709). Terminal products are transport wraps for white goods, beverage containers, and insulation materials. The main field failure mode is puncture at sharp pallet edges and nail heads, which is evaluated by ASTM D5748 after stretching.

Inside FIBC liner production, a 120–200 µm three-layer blown film places FLEXUS VLDPE 5020 in the core layer to decouple puncture resistance from surface sealing and printability. The outer layers are formulated with 0.918–0.926 g/cm³ LLDPE or LDPE for corona adhesion, hot-air weldability, and coefficient of friction control. The core layer represents 50–60 wt% of the total film and is compounded from 80–100 wt% VLDPE 5020 with 0–20 wt% LLDPE to adjust melt strength. Fabrication on a 75 mm/90 mm/75 mm three-extruder line with 30:1 L/D barrier screws and a 500 mm die uses core melt temperatures of 185–200°C; higher temperatures reduce gel formation but can lower bubble stability at the high thickness. Puncture resistance measured by ASTM D5748 is the controlling specification because the liner must withstand impact from irregular mineral particles during FIBC filling. The low-density core absorbs puncture energy while the higher-density skins prevent surface blocking and maintain weld integrity at spout and fill neck areas. Field failure reports indicate that most punctures occur at folded gusset corners where orientation is highest, so a minimum corner thickness of 80 µm is specified by end users. The terminal product is an FIBC inner liner for calcium carbonate, carbon black, and aluminum-silicate minerals. Published data for this specific configuration is limited.

Silage Wrap Blown Film and Oxygen Ingress Control Without Barrier Polyamide

Agricultural silage wrap and bale wrap films require high puncture resistance and stretchability without adding an EVOH or polyamide barrier layer. FLEXUS VLDPE 5020 is used as a toughness modifier in a five-layer blown film where ethylene-vinyl acetate copolymer or a metallocene VLDPE skin provides surface tack. Total thickness is typically 25–35 µm; the VLDPE-containing layer represents 30–45 wt% of the structure. Extrusion is performed with a 1.8–2.0 mm die gap, blow-up ratio 2.5–3.0, and a low frost line to preserve cling. Light stabilization requires 0.8–1.2 wt% of a HALS masterbatch; poor dispersion of the HALS in the VLDPE layer can create gel specks that initiate puncture failure. Oxygen permeability is measured by ASTM D3985; without a barrier polymer the film presents only moderate oxygen barrier, so the film is limited to ensiling conditions where anaerobic fermentation is rapidly achieved. Terminal products are round bale wrap, square bale wrap, and bunker silo cover film. The main processing constraint is the trade-off between cling and unwind speed: too much cling causes stretching in the bale wrapper, while too little causes edge lift under wind.

Medical device pouch films produced for gamma-sterilized barrier pouches use a peelable sealant layer whose seal strength must remain below the tear strength of the underlying substrate. FLEXUS VLDPE 5020 is blended with 20–40 wt% LDPE or polybutene to reduce seal strength to a controlled peel range, typically 3–8 N/25 mm when sealed against uncoated poly or Tyvek. The blown film line uses a 1.4–2.0 mm die gap and melt temperatures of 160–185°C. Seal strength before and after gamma irradiation of 25–40 kGy is evaluated by ASTM F88/F88M, and package integrity is validated under ISO 11607-2. Radiation resistance may vary with the formulation; published data for FLEXUS 5020 under gamma exposure is limited, so each pouch design must be validated under ISO 11137. A narrow seal temperature range is required to prevent fiber tear on Tyvek peel. The terminal product is a clean-peel medical pouch for single-use devices.